This invention relates to a shock and vibration sensitive switch used to detect the presence of unwanted intruders.
Shock and vibration sensitive switches are well known in the art. Such switches are used in burglar alarm type systems and are mounted on a wall or a fence in order to detect the shock and vibrational waves which accompany the approach of an intruder. Such devices normally comprise an inertia weight which is supported by two or more electrical contacts. The weight completes an electrical circuit between the contacts when the switch is in an quiescent state, but the presence of shock or vibrational waves causes the weight to bounce off of the contacts, thus, interrupting the circuit. This interruption is detected by suitable electronic means and an alarm is sounded.
Inertia switches are prone to malfunction because of non-conducting films which form on the surface of the contacts and the inertia weight, thus preventing the weight from establishing the desired closed circuit condition. Additionally, minute particules of plastic or other foreign material which are present in the switch case may accumulate on the conductive surfaces and interfere with the normal operation thereof. Moisture and air-borne contaminants may enter the switch case and initiate corrosion of the metallic elements. It would be desirable, therefore, to provide a shock and vibration sensitive switch which would be resistant to such failure.